This project will examine: 1) the kinetics of inhibition of pancreatic exocrine secretion by exogenous pancreatic polypeptide (PP) and somatostatin, the patterns of release of these peptides by a meal and components of food, and the existence of inhibition produced by intestinal amino acids; 2) release of cholecystokinin (CCK) by a meal and components of food, measured by a specific radioimmunoassay; and 3) the structure-activity relations of several CCK analogs for gastric and pancreatic secretion and gallbladder contraction. In the first study the pancreatic response to meals containing different amounts of protein, fat and carbohydrate will be determined; the effect of intraluminal amino acids on stimulated pancreatic secretion will be measured; the effects of exogenous PP and somatostatin on pancreatic responses to exogenous secretin caerulein, bethanechol and to intestinal perfusion with HCl, amino acids, and sodium oleate will be determined; and the release of PP and somatostatin by these exogenous and endogenous stimulants will be measured. In the second study a specific radioimmunoassay will be used with affinity chromatography to characterize the magnitude, time course, and molecular species of the CCK response to a meal and to intestinal stimulants. In the third study the relative potencies of several sulfated and unsulfated analogs of CCK (CCK8, CCK10, CCK12, CCK14, CCK33, CCK39) for gastric acid secretion, pancreatic enzyme secretion, and gallbladder contraction will be determined using radioimmunoassay to allow characterization of actual delivered dose and circulating levels achieved.